EASTON, Pa.—An eastern Pennsylvania jury has convicted a man of assaulting a child three years ago, rejecting his defense that he could not have committed the crime because medications he was taking caused erectile dysfunction.

Jurors in Northampton County Court deliberated for three hours Friday before convicting 50-year-old Russell Wallery of Moore Township of rape of a child, involuntary deviate sexual intercourse, and corruption of minors.

Prosecutors said he attacked a 10-year-old girl, who is mildly mentally disabled, from July 2007 to January 2008. Wallery testified that he has been impotent since 2006 due to heart problems and diabetes. But prosecutors said the girl would be incapable of maintaining her story so consistently if it was not the truth.

Wallery will be sentenced Sept. 13. Earlier, he pleaded guilty and later pleaded no contest in the case, but withdrew both pleas.